3.3Timber preservation (natural solid timber)

This chapter gives guidance on meeting the Technical Requirements for the protection of natural solid timber against fungal decay when exposed to damp conditions and against insect attack.

Definitions for this chapter

For the purposes of this chapter, the following definitions apply:

Durability to biological
Inherent resistance of a wood species or a wood-based material against wood decay organisms.
HeartwoodInner zone of wood that, in the growing tree, has ceased to contain living cells or to conduct sap.
SapwoodOuter zone of wood that, in the growing tree, contains living cells and conducts sap.
(The durability of sap wood is minimal whatever the species).
Service situationSituation of exposure of the wood element in use.
SoftwoodsAre typically mixture of wood types including juvenile wood, and would contain a high percentage
of sapwood, which may be difficult to distinguish from the heartwood and it is usually impractical
and uneconomical to exclude it.
User classesAre based on differences in environment exposures that can make the wood or wood-based
products susceptible to biological deterioration. Table 1 of BS 8417 summarizes the user class
system and gives examples of typical service situations.
Wood speciesTrade name according to EN 13556 which can on occasion include more than one botanical
tree species.


This chapter gives acceptable treatment schedules for the treatment of natural solid timber but does not cover:

  • products such as plywood and wood particle boards
  • the condition before the treatment
  • treatment process techniques, which is the responsibility of the organisation carrying out the operation.